A high degree of interest has been shown over the past years in the field of theft detection using electronic article surveillance systems wherein magnetically sensitive devices, known as markers, are introduced into a time varying magnetic field, known as an interrogation zone, to emit a signal in response to such magnetic field. Electronic article surveillance (EAS) systems and markers for use therein were disclosed by P. A. Picard in French Patent Number 763,681 (1934). Generally, certain ferromagnetic alloys exhibit high magnetic permeability and low coercivety thereby making their use as EAS marker attractive. Materials for such markers have been made as disclosed in U.S. Pat. Nos. 4,581,524 and 4,568,921 and U.S. Patent application having Ser. No. 290,547. Although these markers generally work well, without the ability to deactivate such markers, i.e., rendering then unresponsive in an interrogation zone, the use of EAS systems becomes limited. For example, when an article with a marker attached thereto is purchased in a first store and the purchaser subsequently enters a second store with the article bearing the marker, the marker could generate an alarm in the EAS system of the second store unless measures are taken to avert the same. As is generally known, there are walk around systems as used in institutions such as libraries where the books are checked out. Thereafter, the individual walks through the gates of the EAS system without the book and is then given the book as it is passed around the gates. Although this system works well in controlled areas, such as libraries, it is not adequate in the commercial use of EAS systems.
In U.S. Pat. No. 3,747,086, a deactivable marker is described that has a soft magnetic strip which is detectable in an interrogation zone of an EAS system. In addition to such soft magnetic strip, two hard magnetic strips sandwich the soft magnetic strip and these have distinctive magnetic properties which are not the same as the detectable soft magnetic strip. After a marker has been used for the purposes of theft detection, it is then magnetized by placing the marker in a magnetic field of high strength to magnetize the two hard magnetic strips elements thereby rendering the marker undetectable. Although this marker functions adequately, as required, it requires a proper orientation of the marker during deactivation because of the anisotropic nature of the configuration. Furthermore, such a scheme does not lend itself to deactivating soft ferromagnetic fibers. In addition, use of such a large amount of hard magnetic material is expensive.
It clearly would be advantageous to provide an EAS marker that can be readily deactivated in a magnetic field without concern as to orientation of the marker during deactivation, particularly where the soft magnetic elements are in the form of a fiber.